Re: Not receiving emails from a specific email address suddenly

I wonder if your issue could somehow be related to the one I posted about recently (MS Mail servers claim Hotmail domain does not exist | Microsoft Community Hub)?  Although you'd have thought in your case the sender should be receiving an NDR (non-delivery report) to explain the failure with the email to you.  In my case the senders that fail to email me are varied, but sometimes the same sender can fail a few times in a row.